1. Field of the Invention
The present invention relates to an electronic component and, more particularly, to an electronic component incorporating a resonator.
2. Related Background of the Invention
Mobile communication devices typified by cell phones are in remarkably widespread use in these days and are rapidly being downsized. In conjunction therewith, components used in the mobile communication devices are demanded to be more downsized and sophisticated.
A branching filter (electronic component) is used for branching or generation of a transmitted signal and a received signal in such mobile communication devices. An example of the branching filter is one comprised of a band-pass filter, a band-stop filter, or a combination of these, and another example of the branching filter for achieving further downsizing and sophistication is one comprised of two filters (resonators) having mutually different band center frequencies.
FIG. 8 shows a functional configuration of a branching filter using two filters with different band center frequencies. In the branching filter (electronic component) 10 shown in FIG. 8, a phase matching circuit 13 is connected to a second filter 12, and matching between impedance characteristics of two filters 11, 12 is made by change of phase. The first filter 11 and the phase matching circuit 13 are connected to a branch point A at an extension from a common terminal C. Input/output terminals S1, S2 for branched signals are connected to the first filter 11 and to the second filter 12, respectively.
FIG. 9 shows a structure of a conventional branching filter for implementing the functional configuration shown in FIG. 8. The branching filter 100 shown in FIG. 9 consists of five layers. This branching filter is comprised of a first filter 11, a second filter 12, a mounting substrate 14, a frame 15, and a shield lid 16. The first filter 11 and the second filter 12 are mounted on the mounting substrate 14. The frame 15 is attached to the mounting substrate board 14 so as to surround the filters 11, 12. The shield lid 16 is fixed to the frame 15 to seal the filters 11, 12 in.
The mounting substrate 14 has a first principal surface 14a and a second principal surface 14b. A common terminal C, input/output terminals S1, S2 (the input/output terminal S1 of which is not shown), and a ground terminal (not shown) are formed on the first principal surface 14a. The filters 11, 12 are mounted on the second principal surface 14b. Two ground layers 17a, 17b are formed in the mounting substrate 14 so as to sandwich a phase matching circuit 13 in the stack direction. Furthermore, a via electrode 18 is formed in the mounting substrate 14. The via electrode 18 is constructed of an electric conductor placed inside a through hole opening at one end in the first principal surface 14a and also opening at the other end in the second principal surface 14b. The via electrode 18 is connected to the common terminal C on the first principal surface 14a and is connected through a bonding pad to the first filter 11 by a bonding wire 19 on the second principal surface 14b. Furthermore, one end of the aforementioned phase matching circuit 13 is connected to a halfway position of the via electrode 18, i.e., a branch point A, and the other end to the second filter 12.
The connection of the filters in the branching filter having the phase matching circuit is described, for example, in Japanese Patent Application Laid-Open No. 2002-237739.